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  1. #1
    Join Date
    Jul 2012
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    Jewett Under counter

    I have a Jewitt Thermo Scientific under counter refrigerator. What is the minimum temperature differential setpoint I can use?
    I have the temp set a 3C, with a 3C deadband. I timed it, and it was 6 minutes between cycles. I am concerned if I lower it to 2C I may short cycle my my compressor. Basically, Im trying to maintain a tight temperature swing.
    Am I already as low as i can go, or should I go lower like 3/5?

    It cools IcePacks, Basically its near 40F. They want a real constant temp, but I dont think my model offers that, (No capacity control, etc).

  2. #2
    Join Date
    Oct 2011
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    Chicagoland Area
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    There's nothing really special about those units except all parts, aside from the condensing unit parts, can only be bought from the mfg and they are awfully expensive. There's a defrost built into the board so you don't have to worry about freezing the coils. Do they have a temperature monitor connected to it? If so, you can drop the temp and check it in a day or two to see if you are getting the desired results.
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

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  3. #3
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    Jul 2012
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    I did that, but they want a tighter reading. I just dont want the compressor cycling every 3 minutes.

  4. #4
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    Oct 2011
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    They're friggin ice packs. Why such a tight tolerance?
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  5. #5
    Join Date
    Jul 2012
    Location
    Southwest
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    Thats what im trying to tell them. They cool an important product, but they dont understand the icepacks maintain a constant temp.

  6. #6
    Join Date
    Feb 2004
    Location
    British Columbia, Canada
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    521
    I used to work on four older jewetts that were used in hospital labs. They were used for blood bank storage. Temp range for blood is 2-8 degC. 40degF or 4degC is ideal as it is in the middle of that zone.

    Everytime the door was opened the sensor for the recording thermometer would follow the air temperature and the lab staff would panic as they did not understand holdover capacity of the product.

    As the blood bags held 250ml (one cup), I built a 250ml sealed vial with 10% glycerol solution to simulate the specific gravity of the blood. This showed the exact temperature of the blood as demonstrated by the flatline on the circular recording chart.

    As long as you have the compressor cycling to keep the temperature on the chart constant you can probably have a 3 to 5 degree span if the cut-out temp is low enough. I would set it for 3deg C cut-out and cut-in at 6deg C to start and then modify it from there to ensure no shortcycling.

    A quick test for you to prove this is to use about a 3oz ball of sealing gum or duct putty to cover the sensor or bulb.

    If your Jewett has multiple temp sensors they may already be in small liquid filled vials.

    Don't mention what you have done to the staff or they may think it is not a real fix. Trust me, it is if the rest of the refrig system is working properly.

    Let me know how it goes.
    Last edited by koolkahuna; 09-14-2012 at 11:50 AM. Reason: Wrong number entered.

  7. #7
    Join Date
    Feb 2004
    Location
    British Columbia, Canada
    Posts
    521
    By the way, what is the product they are using unfrozen icepacks to transport with?

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